The present invention relates to non-woven fabrics having novel structures. An object of the present invention is to provide new materials by using non-woven fabrics. The fabrics with unique three-dimensional structures, wherein at least one junction portion is positioned in the internal portion thereof.
Microorganism-fixing carriers made of non-woven fabrics on which microorganisms are adhered and are allowed to propagate have heretofore been used for treating waste water and as a microorganism reactor for industrial uses, as disclosed in Unexamined Published Japanese Patent Application (Japan Kokai) Nos. 209787/1988, 229857/1989 and 38299/1991. The microorganism-fixing carriers made of non-woven fabrics have excellent capacity for carrying microorganisms since the non-woven fabrics have porous structures. However, they tend to be easily loaded due to the formation of a film of microorganisms that are propagated, and thus a limitation is imposed on the amount of microorganisms that can be carried. Furthermore, the contact area between the microorganisms and the liquid, such as waste water that is to be treated by the microorganisms, is small.
As a microorganism-fixing carrier, there has been proposed a cord-like contact material (Biocord.TM. manufactured by TBR Co., Japan) that employs braided cord technology. However, the cord-like contact material is manufactured through complex manufacturing steps with low productivity and at a high cost, without yielding large contact area. Moreover, this material has a defect in that it tends to be easily deformed.
In an attempt to increase the amount of microorganisms that can be carried and to increase the contact areas, the present inventors have studied the use of a cylindrical, three-dimensional, non-woven fabric that is obtained by flatly or spirally winding a non-woven fabric.
However, the cylindrical, three-dimensional, non-woven fabric obtained by winding a sheet-like non-woven fabric has a weak tensile strength, and is broken or is deformed when a strong tensile force is applied thereto during use of the fabric. Moreover, the fibers that are chiefly oriented in the circumferential direction lack resistance against compression. Besides, aerobic bacteria propagate only on the surface portion of the non-woven fabric. Even when the non-woven fabric is obtained in a three-dimensional form, therefore, the interior of the non-woven fabric is not sufficiently utilized, making it difficult to increase the amount of microorganisms that are carried thereon or to sufficiently increase the contact area with respect to the liquid to be treated.
There have further been proposed: (1) a spherical and solid non-woven fabric which is obtained by packaging a fiber in a spherical mold and fixing it by using an adhesive agent or with an adhesive fiber or by molding a bulky non-woven fabric or fiber webs under the application of heat and pressure, followed by cutting the mold into a sphere; and (2) a coupled bulky ball-like structure obtained by converging and fixing bundles of bulky fibrous yarns at a predetermined interval, as disclosed in Unexamined Published Japanese Patent Application (Japan Kokai) No. 27138/1991.
Like the aforementioned cylindrical three-dimensional non-woven fabrics, however, these three-dimensional non-woven fabrics lack tensile strength, and are subject to be broken or deformed when a strong tensile force is applied thereto during use. These fabrics also fail to exhibit a restoring property after being compressed, and impose limitations on the amount of carried microorganisms and on the contact areas.
Furthermore, a three-dimensional non-woven fabric has been desired even in other fields for such uses as, for example, laces, ornamental products made of fibers, and wadding. However, the cylindrical three-dimensional non-woven fabric obtained by winding the non-woven fabric or the spherical three-dimensional non-woven fabric obtained by packaging the non-woven fabric in the mold and fixing it by using an adhesive agent or an adhesive fiber, still has weak tensile strength and is subject to be broken or deformed when a strong tensile force is applied thereto during use. Such non-woven fabrics have continuous surfaces that only slightly absorb external force, give hard feeling to the touch, and are distorted upon bending. Moreover, the fibers that tend to be oriented in the circumferential direction exhibit small resistance against the compression and fail to restore the fabric to its initial shape after being compressed.